This invention relates to materials useful for hydrogen storage, their use in forming further, densified or compacted, products useful for hydrogen storage and safe transport as well as processes for accomplishing their production and safe storage and transport.
A patent entitled xe2x80x9cA Hydrogen-Based Ecosystemxe2x80x9d filed Nov. 22, 1999, U.S. Pat. No. 6,305,442 (""442), having common assignment and inventors with this application describes new magnesium-based hydrogen storage alloys with high hydrogen charge/discharge kinetics and remarkably high hydrogen storage capacity. Such material provides the basis for an entire national and international infrastructure based upon that inventive newly developed hydrogen storage capacity and means for using such materials made available by hydrogen storage alloys which have surmounted the chemical, physical, electronic and catalytic barriers previously believed to have been insoluble. Such alloys are fully described in U.S. Pat. No. 6,193,929 (""929), entitled xe2x80x9cHigh Storage Capacity Alloys Enabling a Hydrogen-Based Ecosystemxe2x80x9d, filed Nov. 6, 1999 for Ovshinsky et al. That patent relates generally and specifically to alloys which solve the, up to now, unanswered problem of having sufficient hydrogen storage capacity with exceptionally fast kinetics to permit the safe and efficient storage of hydrogen to provide fuel for a hydrogen-based economy. The invention herein described takes the advancements of the previously mentioned patent, as well as other useful hydrogen storage materials and advances the art to the next level by making hydrogen storage materials safer, and more easily handled, transported, and used. The revolutionary breakthrough to provide the enhanced storage and kinetic combination became possible only by considering the materials as a system in which chemical modifiers and the principles of disorder and local order, as pioneered by Stanford R. Ovshinsky (one of the instant inventors), in a manner to provide the necessary catalytic locally ordered environments. Such use of the Ovshinsky principles include the design of surfaces for high kinetic and catalytic activity while at the same time, designing bulk characteristics for high levels of storage capacity and high rate charge/discharge cycling. In other words, these principles allowed for tailoring of the material by controlling the particle and grain size, topology, surface states, catalytic activity, microstructure, and total interactive environments for storage capacity. The invention of highly kinetic high capacity hydrogen storage materials made possible the hydrogen ecosystem, planning for which created the needs which are met by the practice of the current invention as described herein.
Fuel types and choices about them made over the past several generations in the industrialized nations of the world have created problems which, colloquially, are now xe2x80x9ccoming home to roostxe2x80x9d.
As the world""s population expands and its economy increases, the atmospheric concentrations of carbon dioxide are warming the earth causing climate change. However, the global energy system is moving steadily away from the carbon-rich fuels whose combustion produces the harmful gas. Experts say atmospheric levels of carbon dioxide may be double that of the pre-industrial era by the end of the next century, but they also say the levels would be much higher except for a trend toward lower-carbon fuels that has been going on for more than 100 years. Furthermore, fossil fuels cause pollution and are a causative factor in the strategic military struggles between nations. Furthermore, fluctuating energy costs are a source of economic instability worldwide
For nearly a century and a half, fuels with high amounts of carbon have progressively been replaced by those containing less. First wood, which is high in carbon, was eclipsed in the late 19th century by coal, which contains less carbon. Then oil, with a lower carbon content still, dethroned xe2x80x9cKing Coalxe2x80x9d in the 1960""s. Now analysts say that natural gas, lighter still in carbon, may be entering its heyday, and that the day of hydrogenxe2x80x94providing a fuel with no carbon at allxe2x80x94may at last be about to dawn. As a result, experts estimate the world""s economy today burns less than two-thirds as much carbon per unit of energy produced as it did in 1860, despite the fact that carbon based duels are still being used by the automotive industry.
In the United States, it is estimated, that the trend toward lower-carbon fuels combined with greater energy efficiency has, since 1950, reduced by about half the amount of carbon spewed out for each unit of economic production. Thus, the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis of the system. It had been predicted that this evolution will produce a carbon-free energy system by the end of the 21st century. The present invention shortens that period to a matter of years. In the near term, hydrogen will be used in fuel cells for cars, trucks and industrial plants, just as it already provides power for orbiting spacecraft. But ultimately, hydrogen will also provide a general carbon-free fuel to cover all fuel needs.
As noted in recent newspaper articles, large industries, especially in America, have long been suspicious of claims that the globe is warming and have vociferously negated the science of climate change. Electric utilities, among others, initially took the position that international treaties on climate change would cut economic growth and cost jobs. A dramatic shift has now occurred, in which the problems are acknowledged and efforts are now being made to solve them. Therefore, it is very encouraging that some of the world""s biggest companies, such as Royal Dutch/Shell and BP Amoco, two large European oil firms, now state plainly what was once considered heresy: global warming is real and merits immediate action. A number of American utilities vow to find ways to reduce the harm done to the atmosphere by their power plants. DuPont, the world""s biggest chemicals firm, even declared that it would voluntarily reduce its emissions of greenhouse gases to 35% of their level in 1990 within a decade. The automotive industry, which is a substantial contributor to emissions of greenhouse gases and other pollutants (despite its vehicular specific reductions in emissions), has now realized that change is necessary as evidenced by their electric and hybrid vehicles. In this field, the assignee of the subject invention, has developed the Ovonic nickel metal hydride battery, the enabling battery making electric and hybrid vehicles possible.
While hydrogen has wide potential application as a fuel, a major drawback in its utilization, especially in mobile uses such as the powering of vehicles, has been the lack of an acceptable lightweight hydrogen storage medium. Storage of hydrogen as a compressed gas involves the use of large and heavy vessels. Thus, as shown in FIG. 1, compressed hydrogen at 5000 psi only has a hydrogen density of 31 g/liter. Additionally, large and very expensive compressors are required to store hydrogen as a compressed gas and compressed hydrogen gas is a very great explosion/fire hazzard.
Hydrogen is the xe2x80x9cultimate fuel.xe2x80x9d In fact, it is considered by most to be xe2x80x9cTHExe2x80x9d fuel for the next millennium, and, it is inexhaustible. Hydrogen is the most plentiful element in the universe (over 95%). Hydrogen can provide an inexhaustible, clean source of energy for our planet which can be produced by various processes which split water into hydrogen and oxygen. The hydrogen can be stored and transported in solid state form. For example, economical, lightweight, triple-junction amorphous silicon solar cells solar cells (an invention pioneered by Stanford R. Ovshinsky, one of the instant inventors) such as those set forth in U.S. Pat. No. 4,678,679, (the disclosure of which is herein incorporated by reference) can be readily disposed adjacent a body of water, where their inherently high open circuit voltage can be used to dissociate water into its constituent gases, and collect the hydrogen so produced. Also, by placing these high efficiency, lightweight solar panels on nearby farms, in water, or on land. Also, the photovoltaic process for dissociating water to form hydrogen can be a step toward solving the problems of water purification throughout the world. Electricity can be generated to transport and pump the hydrogen into metal hydride storage beds that include the high storage capacity, lightweight metal hydride alloys. The ultra-high capacities of the alloys of the ""497 application allow this hydrogen to be stored in solid form and transported by barge, tanker, train or truck in safe, economical form for ultimate use. Energy is the basic necessity of life and civilization for any society today and the use of hydrogen in the manner described herein as the basic source of energy would minimize the likelihood fought for control of fossil fuels.
In the past considerable attention has been given to the use of hydrogen as a fuel or fuel supplement. While the world""s oil reserves are depletable, the supply of hydrogen remains virtually unlimited. Hydrogen can be produced from coal, natural gas and other hydrocarbons, or formed by the electrolysis of water, preferably via energy from the sun. Moreover hydrogen can be produced without the use of fossil fuels, such as by the electrolysis of water using nuclear or solar energy, or any other form of economical energy (e.g., wind, waves, geothermal, etc.). Furthermore, hydrogen, is an inherently low cost fuel. Hydrogen has the highest density of energy per unit weight of any chemical fuel and is essentially non-polluting since the main by-product of xe2x80x9cburningxe2x80x9d hydrogen is water. Thus, hydrogen can be a means of solving many of the world""s energy related problems, such as climate change, pollution, strategic dependancy on oil, etc., as well as providing a means of helping developing nations.
While hydrogen has wide potential application as a fuel, a major drawback in its utilization, especially in mobile uses such as the powering of vehicles, has been the lack of an acceptable lightweight hydrogen storage medium. Storage of hydrogen as a compressed gas involves the use of large and heavy vessels. Thus, as shown in FIG. 1, compressed hydrogen at 5000 psi only has a hydrogen density of 31 g/liter. Additionally, large and very expensive compressors are required to store hydrogen as a compressed gas and compressed hydrogen gas is a very great explosion/fire hazard.
Hydrogen also can be stored as a liquid. Storage as a liquid, however, presents a serious safety problem when used as a fuel for motor vehicles since hydrogen is extremely flammable. Liquid hydrogen also must be kept extremely cold, below xe2x88x92253xc2x0 C., and is highly volatile if spilled. Moreover, liquid hydrogen is expensive to produce and the energy necessary for the liquefaction process is a major fraction of the energy that can be generated by burning the hydrogen. Another drawback to storage as a liquid is the costly losses of hydrogen due to evaporation, which can be as high as 5% per day. Also, the storage density of liquid hydrogen, as shown in FIG. 1, is only 71 g/liter.
For the first time, storage of hydrogen as a solid hydride, using the atomically engineered alloys of the instant application can provide a greater percent weight storage than storage as a compressed gas or a liquid in pressure tanks. Also, hydrogen storage in a solid hydride is safe and does not present any of the safety problems that hydrogen stored in containers as a gas or a liquid does because hydrogen, when stored in a solid hydride form, exists in it""s lowest free energy state. As shown, again in FIG. 1, storage of hydrogen in a 7% Ovonic thermal hydrogen storage alloy provides a hydrogen density of 103 g/liter, more than 3 times the density of compressed hydrogen gas.
In addition to the problems associated with storage of gaseous or liquid hydrogen, there are also problems associated with the transport of hydrogen in such forms. For instance transport of liquid hydrogen will require super-insulated tanks, which will be heavy and bulky and will be susceptible to rupturing and explosion. Also, a portion of the liquid hydrogen will be required to remain in the tanks at all times to avoid heating-up and cooling down of the, tank which would incur big thermal losses. As for gaseous hydrogen transportation, pressurized tankers could be used for smaller quantities of hydrogen, but these too will be susceptible to rupturing and explosion. For larger quantities, a whole new hydrogen pipeline transportation system would need to be constructed or the compressor stations, valves and gaskets of the existing pipeline systems for natural gas will have to be adapted and retrofitted to hydrogen use, and this is assuming the construction material of these existing pipelines will be suited to hydrogen transportation.
It is a primary objective of the present invention to provide a means of safely and economically transporting hydrogen within a hydride storage material; particularly between a hydrogen generation facility and downstream distributors, but also between such downstream distributors and ultimate or intermediate users, or their combinations. It is understood by those ordinarily skilled in the art that hydrogen storage materials, whether Mg based, rare-earth metal based, or transition metal based, include very small particles composed of much smaller crystallites. Such metals of small size are inherently pyrophoric when exposed to atmosphere. Therefore, shipment of these hydrogen storage materials becomes a safety problem in which it has heretofore been necessary to transport such materials in an inert atmosphere.
Further, the amount of space occupied by a commodity requiring shipping over potentially long distances is a major cost and logistic consideration. The instant inventors originally considered the shipment of the hydrogen in the hydride storage powder itself for all downstream use. Upon reflection and weighing the potential regulatory pitfalls in transportation through interstate or other regulated commerce, the necessity of handling and hydriding the powder at a downstream location as well, as the cost associated with the shipment of large volumes of such powder, the inventors recognized a need to develop a superior transportation system.
Pursuant to the instant invention, the subject inventors have developed such a superior means of transporting hydrogen in hydride storage material over long distances in a safe and economical manner. To begin with, the inventors realized that the pyrophoric material could not be safely handled. The beginning of the solution to the handling problems was initially recognized when they realized that shipment of such hydrogen storage material in a highly hydrided state reduced the possibility of a pyrophoric reaction with the atmosphere. At the same time, it was hypothesized that if the density of the powder could be increased there would be a greatly reduced amount of surface area available for dangerous reactions with atmospheric components. The result was the invention of a high density hydrided pellet that is substantially immune to a pyrophoric atmospheric reaction and which could, therefore, be handled without the burdens associated with a non-reactive environment (generally an inert gaseous atmospheric blanket). Not only does such an invention allow for safe handling by workers, but such products can much more readily meet stringent transportation regulations when transported by on highways by trucks, by rail, by ship, or by air in interstate br other highly regulated commerce.
A further advantage of the hydrogen storage pellet of the instant invention is that the high density is achieved in its hydrided state, therefore, a large weight percent of hydrogen is stored per unit volume. Such notably high storage density substantially reduces the cost per hydrogen unit volume for shipment of that material; i.e.: substantially the same volume of hydrogen storage material can now be shipped with more than twice the weight percent of hydrogen stored therein. If the same volume of material can be shipped with twice the hydrogen stored therein, clearly the cost of shipment is reduced by at least half.
Additionally, we should not lose sight of the significant fact that the hydrogen storage magnesium alloy material which forms a preferred embodiment of the instant invention, in its hydrided powder-state, can already store more than 7 weight percent of that magnesium alloy material as hydrogen as well as discharge and charge the same with excellent rate kinetics.
It should be appreciated, therefore, that the present invention contemplates a method of safely transporting hydrogen in a hydride storage material by providing for shipment of said material as a compacted hydride, preferably in the form of discrete units or compacts, which may be referred to as pellets or tablets, in any one of a variety of possible, equally preferred, shapes. It should be understood that the scope of what is meant herein by xe2x80x9cshippingxe2x80x9d is in no way limited, but is meant to include any transportation of hydrogen within hydride storage material between any and all possible origins and destinations in any manner.
A first object of the present invention is to provide a method of safely, economically transporting hydrogen and hydrogen storage material by shipping said material as a discrete compacted hydrided alloy, preferably of a magnesium alloy and more preferably as a magnesium alloy with mischmetal or its components and also including silicon. The hydrogen storage material is compacted into one or more dense pellets of any size and shape desired by one skilled in the art, but the pellets preferably have a diameter of less than about 2.5 cm (1 inch) and a thickness of less than 4 millimeters, preferably less than 2 millimeters. The density of the hydrided magnesium alloy pellet is greater than 0.8 grams/cc, preferably greater than 1.0 grams/cc, and most preferably greater than 1.2 grams/cc. In a preferred embodiment of the invention, substantially no binder is added to the hydrided storage material or alloy prior to compacting the powdered alloy; the resulting pellets are loaded into bulk transport containers such as cargo transport containers, etc.
A second object of the invention is to provide a compacted hydrided hydrogen storage alloy having a density greater than 55% of its theoretical maximum, preferably greater than 85% of its theoretical maximum, and most preferably greater than 90% of its theoretical maximum. For a magnesium alloy, the density is between 0.8 to 1.45 grams/cc. The alloy is preferably compacted without a substantial amount of binder into pellets. The sizes of the hydrided alloy particles used in compacting the pellets is not of particular importance unless high dehydrogenation kinetics are important, in which case, the powder particles are preferably between 10 to 100 micrometers, and more preferably between about 20-63 micrometers. The pellets are shaped to provide pellet-packing density with less than 30% open. The pellets preferably have a diameter of less than about 2.5 cm (1 inch) and a thickness of less than 4 millimeters, preferably less than 2 millimeters. The magnesium alloy includes at least 2 weight % or more of occluded hydrogen.
A further object of the present invention is to provide a method of processing pyrophoric hydrogen storage material having a particle size between about 100 micrometers and 2 millimeters, grinding the powder, hydriding the ground powder and compacting the hydrided powder to form discrete bodies having a density of greater than about 0.8 grams/cc. After hydriding, the sizes of the hydrided alloy particles used in compacting the pellets is not of particular importance unless high dehydrogenation kinetics are important, in which case, the powder particles are preferably between 10 to 100 micrometers, and, more preferably between about 20-63 micrometers. The un-ground powder may be formed by gas atomization of magnesium alloy material and preferably rotary or centrifugal atomization. The grinding step is preferably performed in an attritor (but other mills, including ball mills may be used) and usefully also includes graphite powder and/or heptane grinding aids there within. The sizing step is preferably accomplished by passing the powder through at least one sieve to obtain the powder fraction having the desired particle size range. The discrete bodies are usefully packaged into bulk transport containers such as cargo transport containers, etc. for shipment.
Yet another object of the instant invention is provide a hydrided hydrogen storage alloy of magnesium that includes particles having a size distribution of 100 micrometers to 2 millimeters. Mischmetal elements are also included in the magnesium alloy, said alloy formed by cooling a melt thereof at a rate within the range of about 103 to 105 degrees C./sec. The magnesium alloy is formed by a rapid quench technique, such as gas atomization (rotary atomization), which provides the required quench rate.
A still further objective of the present invention is to provide a method for comminuting and hydriding a magnesium hydrogen storage alloy that comprises the step of minimizing oxidation of the exposed surfaces of the alloy, such as by conveying the alloy from the comminuter to the hydrider in an inert environment formed of a noble gas such as helium, neon, argon or combinations thereof. The hydrided magnesium alloy comprises particles, said particles sized between 10 and 100 micrometers and preferably between 20 and 63 micrometers and most preferably between about 20 and 37 micrometers.